Method and device for activating functions of a powered-off device via a serial data bus interface

ABSTRACT

A method and device are provided for activating certain functions of a powered-off device having a serial data bus interface when it is attached to a powered device via the serial bus interface. On detection of a voltage on the power line of the serial bus, the processor of the device is booted in a special operation mode, wherein certain functions of the serial data bus interface can be used without powering the complete device. The device may then be enumerated by the attached host device and for example allow access to its memory unit or use the power signal on the serial bus interface for battery charging.

RELATED APPLICATION

This application was originally filed as PCT Application No.PCT/IB2006/002661 filed Sep. 26, 2006.

FIELD OF THE INVENTION

This invention relates to a device having a serial data bus interface,and in particular to a device and a method for activating certainfunctionalities of such a device via its serial data bus interface whenpowered off.

BACKGROUND ART

Many electronic devices are arranged to be connected to another device,such as a personal computer, laptop computer, or a printer, for datacommunication. Some examples for such devices are handheld computers,digital cameras, media players, or mobile phones. The connection to a PCor some other device is frequently effected via a serial datacommunication bus.

A serial data bus interface usually includes at least one data line, aground line and a power line. Additional pins and lines may be present.In most cases a device is allowed to draw power from the power line onthe interface. The purpose of this power supply is that devices withlimited power consumption would not need to have an additional powersupply for operation with the host device. For the example case of theUniversal Serial Bus (USB) standard, specifications define how muchpower may be consumed by a device and under what conditions power may bedrawn. Usually a specific connection procedure compliant with arespective standard is required before the serial bus can be used fordata communication or for supplying power.

As most devices as mentioned above use a battery or rechargeable batteryas a mobile power source, power consumption and recharging of batteriesare important design considerations. The power supplied on a serial databus might be used to recharge a battery utilizing the same interface andconnection that are used for data communication through the bus.

A variety of electronic devices include some security or authenticationlock, such as a personal identification code or password a user has toenter before he can access and utilize the device. This is a commonfeature for e.g. mobile phones, where a security lock is usuallyimplemented via a numerical PIN code that has to be entered when thephone is powered on. If a user does not enter a valid PIN code, thevarious functions of the phone cannot be used.

If a user only needs limited access to a device, it is not alwaysnecessary to provide complete functionality for all units and elementsof the device. For example, charging of an internal device battery ortransferring data from the device memory via the serial bus interfacedoes not require complete access to all functions and processes thedevice is capable of Besides the fact that handling would be easier andfaster (for both the user and an external device connected for chargingor data transfer) when no elaborate activation procedures have to befollowed, also power consumption may be considerably lower when onlypart of a device is activated. However, to access and use a serial databus interface such as USB, the device has to be powered on as describedto be able to authenticate or initializes according to any predefinedstandard procedures.

SUMMARY OF THE INVENTION

A method is provided for a powered-off device for entering a deviceoperation mode with special functionality upon connecting a powereddevice via a serial data bus.

This is in one embodiment achieved by a method comprising connecting apowered-off first device to a second device via a serial data businterface, said first device being operable in at least a full firstoperation mode and a second operation mode; providing a voltage fromsaid second device to said first device via said serial data businterface; said first device detecting said voltage provided at saidinterface; activating a processing unit of said first device in responseto said detected voltage; and entering said second operation mode insaid first device. This allows a non-powered device to be partlyactivated in response to a power signal detected on its serial data businterface, not requiring any further activation procedure from a user.The second operation mode may e.g. be a limited operation mode,providing only reduced functionality of the device compared to the firstfull mode, or a operation mode providing partially or completelydifferent functions than the standard operation mode.

In certain embodiments, said initializing of a second operation mode insaid first device further comprises communicating a set of parameters tosaid second device; and receiving a selected one of said set ofparameters from said second device. These parameters may e.g. be usedfor configuration of the device.

According to exemplary embodiments of the invention said set ofparameters includes at least one current value, which could be used toconfigure for a battery charging process.

In various embodiments of the invention, the method further comprisesinitializing data communication between said first and second devicesvia said serial data bus interface. Such a initialization is for exampleknown in the USB standard as enumeration, but may also be present in anyother serial bus communication.

In some embodiments the serial data interface may be operated accordingto the Universal Serial Bus Standard and initializing of datacommunication may comprise an enumeration according to the UniversalSerial Bus standard. This standard is widespread for mobile and fixedterminals to allow for easy data communication between devices.

According to exemplary embodiments, said enumeration is performed inaccordance with the USB mass storage device class protocols. Theseprotocols are also supported by a large number of devices and ensureeasy memory storage access via the USB connection.

Optionally said second operation mode may comprise providing access to amemory element of said first device; and enabling data communication ofdata stored at said memory element to said second device via said serialdata bus interface.

Furthermore, said second operation mode may in certain embodimentscomprise activating at least part of a visual display element; anddisplaying a current state of at least one functionality that isprovided in said second operation mode. The state of such afunctionality may be shown as a symbol that a user may identify, by atext or optionally by a combination of both.

In some embodiments of the invention the charging level of arechargeable battery of said first device is indicated on said visualdisplay element. The indication may include a scroll bar or a chargingsymbol, or some other continuous or non-continuous information about thecharging process and/or the current battery level.

In various embodiments, presence of an ongoing data communication viasaid serial data interface is indicated on said visual display element.This allows a user to see that data is currently transferred such thathe will not detach the connection.

The method according to some embodiments of the invention may furthercomprise initiating a charging process for a rechargeable battery ofsaid first device, wherein said charging process uses a current suppliedby said second device via said serial data interface.

Optionally said charging process may be performed using said receivedselected one of said set of current values as a maximum chargingcurrent. Thus, the connected device may choose the most suitable valueand the charging will then be performed according to the selected value.

As a further aspect of the invention, a computer program product storedon a computer readable medium is provided, arranged to perform any ofthe method steps as stated above when executed on a processor.

According to another aspect of the present invention, a device isprovided comprising: a serial data bus interface, including a powerline, a ground line and at least one data line; a processing unit; acontrolling unit capable of detecting a voltage at said power line in apowered-off state of said device, and further capable of activating saidprocessing unit in a second operation mode in response to a detectedvoltage.

The device may in some embodiments further comprise at least one datastorage unit, wherein said second operation mode is arranged to enableaccess for an external device to said data storage unit via said serialdata bus interface.

Certain embodiments of the device may further comprise a memory cardslot, wherein said data storage unit is a removable memory card operablyinserted into said memory card slot.

Alternatively or additionally, said data storage unit may be anintegrated memory element of said device in various embodiments of theinvention. This could be a integrated flash memory, a hard drive, orsome other fixed volatile and/or non-volatile memory element.

According to exemplary embodiments of the invention the device maycomprise a rechargeable battery, and an energy management unit connectedto said battery and said processor, and arranged to initiate and controla charging process for said rechargeable battery.

In some embodiments said energy management unit comprises circuitrycapable of connecting or disconnecting said battery to said power lineof said serial data bus interface. This will allow the energy managementto start and stop a charging process when appropriate conditions aremet.

Exemplary embodiments of the device may further comprise a visualdisplay connected to said processor, and said display may be arranged toindicate a current state of at least one functionality provided in saidsecond operational mode.

The device may according to some embodiments further comprise a radiocommunication unit for communicating in a cellular network. A cellularcommunication device could thus also be activated in part by its serialdata bus interface.

In certain embodiments of the invention said radio communication unit isarranged to remain deactivated in said second operation mode. Thus, onlynecessary functions are activated and the radio communication unitcannot be accessed in this mode.

According to exemplary embodiments of the invention said serial data businterface is operated according to the Universal Serial Bus Standard.

As another aspect of the invention, a device is provided comprising aprocessing means; means for connecting to a second device via a serialdata bus interface; means for detecting a voltage provided at saidserial data bus interface in a powered-off state; means for activatingsaid processing means in response to said voltage detecting; and meansfor entering a second operation mode.

Some embodiments of the device may further comprise means for indicatinga voltage state of at least one functionality that is provided in saidsecond operation mode. The indicated state may e.g. be a batterycharging level, a data transmission indication or some otherinformation.

BRIEF DESCRIPTION OF FIGURES

In the following, exemplary embodiments of the invention will bedescribed in more detail, with reference to the accompanying figures,wherein

FIG. 1 is a schematic representation of an exemplary device according tothe invention, and

FIG. 2 shows a flow chart of an exemplary method according to theinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following, some exemplary embodiments of the invention will bediscussed in more detail. In certain cases, explanations will be givenwith regard to USB (Universal Serial Bus) interfaces as a common exampleof a serial data bus. However, all features and procedures also apply todevices having and methods using any other serial data bus interface.The invention is not limited to any specific standard, device type anddesign, or interface implementation.

FIG. 1 illustrates a schematic structure of an exemplary deviceaccording to the invention. A device 2 having a serial data businterface may connect to further devices 4 with similar interfaces fordata signaling and/or power supply. The serial data bus 6 usuallyincludes at least one data line DATA, a power line VBUS and a groundline GND. Further data lines or lines intended for other purposes may bepresent. Each device may connect to a hub such as a device 4 which mayhave a number of downstream facing ports for several devices as well asan upstream facing port in direction of the host. A hub that is includedat the host and provided with a controller, referred to as a root hub,only has downstream facing ports. Devices that do not themselves serveas hubs only provide an upstream facing port. For some serial data busarchitectures, there is not necessarily a host/peripheral structure, buttwo devices with essentially equal capabilities may be interconnected bya serial bus connection. Also, several devices may have both downstreamand upstream bus ports and may then be cascaded. A hub or host may bedesigned as a standalone element for connection to some other device oralternatively be integrated into units such as a personal computer,printer, monitor, or any other suitable apparatus. A hub (or any othersimilar structure) may be self-powered or bus-powered, that is, it maybe powered by its own power supply (self-powered) or through the bus ofthe host device such as a computer. The required power may for examplebe provided via a mains connection or a rechargeable or non-rechargeablebattery.

Features and details for the USB standard, which may be used inexemplary embodiments, are specified in the “Universal Serial BusSpecification”, Revision 2.0 of April 2000, available from the USBimplementers forum, which is hereby incorporated by reference.

Devices with serial data bus interfaces may serve various differentpurposes. They may be used for data processing such as computers andhandheld personal assistants, for media playback of video or audio data,for data storage such as card readers and flash drives, for mobilecommunication such as a cellular phone, and much more. This listing isnot intended to be complete, and many other devices are known in the artthat are or could be equipped with at least one serial data businterface. Therefore, any further elements and units integrated in suchdevices may also differ from case to case. In some embodiments using theinvention, a user interface 14 may be included which may comprisedifferent elements for user interaction. Examples are keypads, buttons,scroll wheels, microphones and elements for speech recognition, or anyfurther means suitable for user inputs; visual display elements and/orspeakers for audio output, or any other means to indicate information toa user.

One or more processing units 8 (processors) may be provided that mayexercise a plurality of functions. They will be used for processingdata, executing software program code modules stored in memory, and ingeneral controlling and conducting many or all of the functions of thedevice. Thus, the central processor 8 is usually connected to many otherunits of a device, such as the user interface 14, data interfaces, orenergy management units 12. Further processing units or controllers maybe included for specific functions of the device (not shown).

To store such software modules and other data permanently ortemporarily, one or more memory elements 16 may be included in thedevice. This may e.g. be a integrated memory comprising software to beexecuted by the processing unit 8 for various device functionalities anddatabases, or removable data storage units such as memory cards. Cardslots may be provided to insert certain types of replaceable memorycards, such that a user can flexibly exchange data between devices andeasily extend storage capabilities of the device. Data may be receivedfrom data communication interfaces on the device and stored in memory,or also retrieved from memory and transmitted via one of the interfacesto some other element.

Usually, a device will include a power supply 10 and/or a interface foran external power supply. An internal power supply may for example be arechargeable or non-rechargeable battery 10 that could optionally bereplaceable. To allow recharging of the battery 10 when integrated intothe device 2, a connection to an external charging interface may beprovided. In case of a serial bus interface 6 having a dedicated powerline VBUS or generally a line that is capable of providing electricalpower, the battery 10 may be connected to this line for chargingpurposes, optionally including further circuit elements. In addition,certain embodiments may comprise a special energy management unit 12that may for example be capable of controlling any aspects of chargingprocesses, power saving and many more. Such an energy management unit 12may include software portions, hardware portions such as integratedcircuits, or a variable combination of both. The energy management unit12 may be coupled between the rechargeable battery 10 and the powerinput interface, and may additionally be connected to the device'scentral processing unit 8 or any other units included in a device.Certain energy management processes may optionally and partially be usercontrolled.

FIG. 2 shows method steps according to various exemplary embodiments ofthe invention. A first device 2 and a second device 4 both having aserial data bus interface are provided. The first device is powered off,while the second one is powered on. As an example, the second device maybe a powered USB hub/host on a personal computer and the first devicemay be a mobile phone having a USB port or another serial port for datacommunication and charging purposes. Now, both devices areinterconnected through their serial data bus interfaces 6 in step 100.Since the second device is active and powered on, it may provide avoltage and current on the power line of the serial bus interface. For aUSB compliant example embodiment, maximum current ratings are given bythe USB standard.

A detection circuit of the first device may then activate certain partsof the first device in response to a voltagedetected in step 102 on theconnected power line of the serial bus port. The entered secondoperation mode may in exemplary embodiments include booting a deviceprocessor (step 104) for executing one or more software elements. Anyelements and units which are not needed for a specific desired functiondo not need to be activated. For example, any user interface elementssuch as display or input elements could remain deactivated or onlyperform limited functions. As a further example, a mobile phone mightnot be allowed to use its radio communication interface. In this secondoperation mode, the processor may also optionally be operated on a lowerclock rate than usual or possible. In exemplary embodiments, the secondoperation mode may not be indicated to a user in any way, such that thedevice would still appear as powered off from the outside since the userinterface including visual display, sound interfaces and furtherelements may be deactivated. Also, certain functions may be activated inthis mode that are not used in standard (first) operation mode.

Next, the first device may in step 106 of FIG. 2 communicate severalcurrent supply options to the connected first device. In the exampleshown, three possible configurations are presented: a very low current,a limited current and a maximum current. In accordance with the currentUSB 2.0 standard taken as an example, the maximum current supplied viathe power line VBus is 500 mA for an enumerated device on a self-poweredhub. 100 mA may be provided in certain other cases, such as on abus-powered hub, where the sum of currents supplied to all connecteddevices may not exceed 500 mA. Thus, in this example 500 mA is given asthe maximum current option, 100 mA as the limited current option and avery low trickle current of 8 mA as a third option. One of the possibleconfigurations may be defined as a default configuration value at thefirst device. To ensure that the device can draw as much power aspossible, the highest value may be defined as a default value, but otherconfigurations and default values are possible as well. In addition tocurrent supply values, other parameters and configuration values may becommunicated. These may e.g. be parameters needed for enumeration or forperforming any functions that should be activated on attaching thedevice to a host/hub. If a connected device cannot provide sufficientcurrent, for example because of further devices attached and limitingthe remaining available current or because it is battery-powered itselfand can inherently only supply a limited current, it may select a lowercurrent value configuration and communicate this option back to thefirst device.

For initializing data communication and to enable all functions providedvia the serial data bus, the device may in certain embodiments berequired to perform an initializing procedure that may be predefined bya standard for the serial bus. Such a procedure may comprisetransmission of predetermined parameters and messages, or e.g. certainlogic voltage signals to indicate the presence of a device capable ofcommunication via the bus. In the USB standard, the initialization thatis triggered by interconnecting two USB compliant devices is referred toas bus enumeration, which is used to identify and manage any devicestate changes as necessary. Configuration values are exchanged and thedevice is assigned an address for communication with the host. Invarious embodiments of the invention and again with reference to theflow chart of FIG. 2, the second device (such as a USB host) willenumerate the first device by selecting one of the configurationsreceived in step 108.

In certain embodiments, a USB device may enumerate (step 110) as a USBmass storage device, that is, using the communication protocolsaccording to the USB mass storage device class. The USB mass storagedevice class provides a convenient interface for accessing data on adevice via a USB connection using e.g. SCSI transparent commands in someembodiments. Since many devices support this protocol class, especiallypersonal computers (PCs) and laptops, this is also an easy way for usingbasic mass storage functionalities of a USB device that may neverthelessbe capable of providing a variety of further USB and non-USBfunctionalities. These further functionalities may or may not be activein the second operation mode that is entered when connecting thedeactivated (unpowered) device. For further details of the mentionedexample of the USB mass storage class, reference is made to the“Universal Serial Bus mass storage class specification overview”, USBimplementers forum, version 1.2 of June 2003, and the respectivespecification documents referenced in this overview. As before, theinvention is not limited to this protocol class or the USB standard, butrather encloses any serial data bus interface. Thus, other protocols andinitializing procedures may be used in those cases without departingfrom the scope of the invention.

This may have various effects. For example, the first device 2 would nowbe able to charge (step 114) its battery using the maximum currentaccording to the used serial bus standard, as it has initializedcommunication in step 110 in a predefined way (such as a USBenumeration) with the power supplying second device. Furthermore, thesecond device 4 may have partial or even full access (step 116) tostorage elements of the first device, such as memory cards inserted in acard slot of the first device. If no card is inserted in such a slot,the device may optionally act as a card reader with an empty card slotfrom the viewpoint of the accessing first device. Similar functions maybe used to automatically update data or software of the first devicewhen connecting it, although it is powered off when the serial interfacecable is attached. A memory card that is inserted in a card slot of thefirst device may be additionally protected by a password, such thataccess is prevented in this case.

Within the first device, the charging and memory access according toexemplary embodiments of the invention may be performed in various ways.As stated above, a device may include several software and hardwaremodules for different functions. A energy management unit 12 maycomprise a software module that provides for charging of the battery andperforms functions concerning energy management, such as chargingalgorithms, overheating protection/monitoring, and so on. It may furthercomprise circuitry, such as application-specific integrated circuits,that are used on the hardware side for charging the batteries, thuscomprising switching circuits, detection circuits and other suitableelements. Detection of the attachment and the voltage supplied on theserial data bus connector may be achieved by detection circuitryimplemented in various ways, such as resistor based detection of highand low logic states, logic gates, and other elements known in the art.

If the battery level of the first device is at first completelydischarged or too low to allow entering of the second operation mode,the device may use the supplied current of e.g. 100 mA maximum forcharging the battery and then automatically start the wake up process ofstarting up the processor and entering the second operation mode asdescribed above when the battery level is above a certain requiredlevel.

Another software based controlling module may be responsible forhandling the detection of an attached host, processing signals of theserial data bus interface, providing communication to the user interfaceabout connections and functions, or to the energy management unit foroptions and configurations regarding e.g. available charging current.Using such a case as an example embodiment, the controlling module maydetermine that a charging possibility is given by an attached device andperform the initialization/enumeration process as described above.Subsequently, the received selected configuration value or values may betransferred from the controlling module to the energy management unit,thus informing the energy management unit of the charging option and themaximum current that may be drawn for charging. In response to thisinformation, the energy management unit may initiate charging of thebattery according to the received current values and further options.Certain embodiments of the invention may include the energy managementunit indicating (step 118 in FIG. 2) a charging state (such as“charging” or “battery fully charged”) as text or a symbol on a displayof the device.

Due to the initialization or enumeration, optionally as a USB massstorage device, the corresponding USB host now has full access to thephone's memory, such as a inserted memory card. It should be appreciatedthat all possible functions as described above are effected without theneed to activate the device by pressing a “on” button or entering anauthentication code. The method as described in the exemplary embodimentis initiated by merely attaching a powered second device to theunpowered and deactivated first device via its serial data businterface.

Many types of devices could use embodiments of the invention. Forexample, a powered-off mobile phone may be connected to a computer via aserial data bus interface and connector such as USB or another standardfor automatically charging its battery and transmitting data stored onmemory card, or for updating data (address book, software, ring tones);access to a memory card may optionally be security controlled bypassword protection for the memory card itself. As another example, apowered-off digital camera attached to a USB port of some other devicemay start up automatically for transmitting data (pictures, video data)stored in internal or removable memory elements, and may optionally (butnot necessarily) charge its battery/batteries at the same time withmaximum available current.

Although exemplary embodiments of the present invention have beendescribed, these should not be construed to limit the scope of theappended claims. Those skilled in the art will understand that variousmodifications may be made to the described embodiments and that numerousother configurations or combinations of any of the embodiments arecapable of achieving this same result. Moreover, to those skilled in thevarious arts, the invention itself will suggest solutions to other tasksand adaptations for other applications. It is the applicants intentionto cover by claims all such uses of the invention and those changes andmodifications which could be made to the embodiments of the inventionherein chosen for the purpose of disclosure without departing from thespirit and scope of the invention.

1. A method comprising connecting a powered-off first device to a seconddevice via a serial data bus interface, said first device comprising aprocessor configured to operate said first device in at least a firstfull operation mode and a second operation mode that has lessfunctionality than the first full operation mode; detecting a voltagereceived from said second device at said first device via said serialdata bus interface; in response to detecting said voltage, booting saidprocessor of said powered-off first device to enter said secondoperation mode and initiating a communication mode for said serial businterface in said second operation mode to initiate a charging processfor a rechargeable battery of said first device, wherein said chargingprocess uses a current supplied by said second device via said serialdata interface, wherein said second operation mode comprises, withoutrequiring a user to switch said first device on, providing at least oneof read and write access to a memory element of said first device viasaid serial data bus interface to enable at least one of (i) datacommunication of data stored at said memory element to said seconddevice and (ii) data communication of data from said second device to bestored at said memory element.
 2. The method according to 1 wherein saidserial data interface is operated according to a Universal Serial BusStandard (USB) and said initiation of a communication mode comprisesinitializing data communication with said second device to perform anenumeration according to the Universal Serial Bus standard.
 3. Themethod of claim 2, wherein said enumeration is performed in accordancewith USB mass storage device class protocols.
 4. The method according toclaim 1, wherein said second operation mode comprises activating atleast part of a visual display element; and displaying a current stateof at least one functionality that is provided in said second operationmode.
 5. The method according to claim 4, wherein a charging level ofthe rechargeable battery of said first device is indicated on saidvisual display element.
 6. The method according to claim 1, whereoperating in the second operation mode comprises operating saidprocessor at a lower clock frequency than when said processor operatesin the first operation mode.
 7. A device comprising a serial data businterface, comprising a power line, a ground line and at least one dataline; said device comprising at least one processing unit configured tooperate said device in a first, full operation mode and a secondoperation mode that has less functionality than the first full operationmode, a controlling unit configured to detect a voltage at said powerline in a powered-off state of said device, and further configured inresponse to detecting said voltage to boot said processing unit so as tooperate said powered-off device in said second operation mode, saidprocessing unit is further configured when said device is operating insaid second operation mode to initiate a communication mode for saidserial bus interface; and an energy management unit connected to arechargeable battery and said processing unit, and arranged to initiateand control when said powered-off device is in said second operationmode a charging process for said rechargeable battery using said serialbus interface after said processing unit initiates said communicationmode for said serial bus interface, wherein said second operation modecomprises, without requiring a user to switch said device on, providingat least one of read and write access for an external device to a memoryelement of said device via said serial data bus interface to enable atleast one of (i) data communication of data stored at said memoryelement to said external device and (ii) data communication of data fromsaid external device to be stored at said memory element.
 8. The deviceaccording to claim 7, further comprising a memory card slot, whereinsaid data storage unit is a removable memory card operably inserted intosaid memory card slot.
 9. The device according to claim 7, wherein saiddata storage unit is an integrated memory element of said device. 10.The device according to claim 7, wherein said energy management unitcomprises circuitry configured to connect or disconnect said battery tosaid power line of said serial data bus interface.
 11. The deviceaccording to claim 7, further comprising a visual display connected tosaid processing unit, wherein said display is arranged to indicate acurrent state of at least one functionality provided in said secondoperation mode.
 12. A device according to claim 7, wherein the initiatedcommunication mode enables said device to receive and negotiate chargingcurrent options on said serial data bus interface.
 13. The deviceaccording to claim 7, where operating in the second operation modecomprises operating said processing unit at a lower clock frequency thanwhen said processing unit operates in the first operation mode.
 14. Amethod comprising connecting a powered-off first device to a seconddevice via a serial data bus interface, said first device comprising aprocessing unit configured to operate said first device in at least afirst full operation mode and a second operation mode that has lessfunctionality than the first full operation mode; detecting a voltagereceived from said second device at said first device via said serialdata bus interface; in response to detecting said voltage, booting saidprocessing unit of said powered-off first device to operate in thesecond operation mode; and negotiating current supply options with thesecond device in said second operation mode for charging a battery ofthe first device and starting charging the battery of the first devicewith the negotiated current from the second device; wherein said secondoperation mode comprises, without requiring a user to switch said firstdevice on, providing at least one of read and write access to a memoryelement of said first device via said serial data bus interface toenable at least one of (i) data communication of data stored at saidmemory element to said second device and (ii) data communication of datafrom said second device to be stored at said memory element.
 15. Amethod according to claim 14, wherein a communication mode for saidserial bus interface is initiated in said second operation mode.
 16. Themethod according to claim 14, where operating in the second operationmode comprises operating said processing unit at a lower clock frequencythan when said processing unit operates in the first operation mode. 17.A device comprising a serial data bus interface, comprising a powerline, a ground line and at least one data line; said device comprisingat least one processing unit configured to operate in a first, fulloperation mode and a second operation mode that has less functionalitythan the first, full operation mode, a battery, said device configuredto detect a voltage at said power line in a powered-off state of saiddevice, and further configured to boot said processing unit so as tooperate said powered-off device in said second operation mode inresponse to a detected voltage, said processing unit being configuredwhen operating in said second operation mode to negotiate current supplyoptions on said serial data bus interface and being further configuredto start charging the battery from the serial data bus interface withthe negotiated current; wherein said second operation mode comprises,without requiring a user to switch said device on, providing at leastone of read and write access to a memory element of said device via saidserial data bus interface to enable at least one of (i) datacommunication of data stored at said memory element to an externaldevice and (ii) data communication of data from said external device tobe stored at said memory element.
 18. The device according to claim 17wherein the processing unit is further configured to initiate acommunication mode for said serial data bus interface in said secondoperation mode.
 19. The device according to claim 17, where operating inthe second operation mode comprises operating said processing unit at alower clock frequency than when said processing unit operates in thefirst operation mode.